Harden the free Render runtime

Dockerfile

@@ -3,7 +3,7 @@
 
 # This Dockerfile is designed for production, not development. Use with Kamal or build'n'run by hand:
 # docker build -t rails_8_template .
-# docker run -d -p 80:80 -e RAILS_MASTER_KEY=<value from config/master.key> --name rails_8_template rails_8_template
+# docker run -d -p 80:80 -e SECRET_KEY_BASE=<generated secret> --name rails_8_template rails_8_template
 
 # For a containerized dev environment, see Dev Containers: https://guides.rubyonrails.org/getting_started_with_devcontainer.html
 
@@ -71,4 +71,8 @@ ENTRYPOINT ["/rails/bin/docker-entrypoint"]
 
 # Start server via Thruster by default, this can be overwritten at runtime
 EXPOSE 80
+
+HEALTHCHECK --interval=30s --timeout=5s --start-period=20s --retries=3 \
+  CMD curl -fsS http://localhost/up || exit 1
+
 CMD ["./bin/thrust", "./bin/rails", "server"]

app/jobs/application_job.rb

@@ -1,4 +1,7 @@
 class ApplicationJob < ActiveJob::Base
+  # Keep enqueue semantics portable even though jobs currently share the primary database.
+  self.enqueue_after_transaction_commit = true
+
   # Automatically retry jobs that encountered a deadlock
   # retry_on ActiveRecord::Deadlocked
 

config/cache.yml

@@ -2,7 +2,8 @@ default: &default
   store_options:
     # Cap age of oldest cache entry to fulfill retention policies
     # max_age: <%= 60.days.to_i %>
-    max_size: <%= 256.megabytes %>
+    # Leave most of Supabase Free's database quota for application data and Solid Queue/Cable.
+    max_size: <%= Integer(ENV.fetch("SOLID_CACHE_MAX_SIZE_MB", 64)).megabytes %>
     namespace: <%= Rails.env %>
 
 development:

config/puma.rb

@@ -33,18 +33,20 @@
 # Allow puma to be restarted by `bin/rails restart` command.
 plugin :tmp_restart
 
-# Run the Solid Queue supervisor inside of Puma for single-server deployments
-plugin :solid_queue if ENV["SOLID_QUEUE_IN_PUMA"]
+# Run the Solid Queue supervisor inside of Puma for single-server deployments.
+if ENV["SOLID_QUEUE_IN_PUMA"] == "true"
+  plugin :solid_queue
 
-# Run Solid Queue in async mode: worker/dispatcher/scheduler run as threads
-# inside the Puma master process instead of being forked into 4 subprocesses.
-# Required on Render's 512MB free plan — fork mode adds ~460MB of process
-# overhead (supervisor + 3 children) and pushes the container into OOM-loop.
-# Async mode collapses that to ~50MB of additional thread overhead in Puma
-# master. Trade-off: less isolation between SQ threads and Puma — a hung or
-# leaky SQ thread affects request serving. For low-traffic student projects
-# the trade-off is right; revisit if upgrading to a paid plan with more RAM.
-solid_queue_mode :async if ENV["SOLID_QUEUE_IN_PUMA"]
+  # Run Solid Queue in async mode: worker/dispatcher/scheduler run as threads
+  # inside the Puma master process instead of being forked into 4 subprocesses.
+  # Required on Render's 512MB free plan — fork mode adds ~460MB of process
+  # overhead (supervisor + 3 children) and pushes the container into OOM-loop.
+  # Async mode collapses that to ~50MB of additional thread overhead in Puma
+  # master. Trade-off: less isolation between SQ threads and Puma — a hung or
+  # leaky SQ thread affects request serving. For low-traffic student projects
+  # the trade-off is right; revisit if upgrading to a paid plan with more RAM.
+  solid_queue_mode :async
+end
 
 # Specify the PID file. Defaults to tmp/pids/server.pid in development.
 # In other environments, only set the PID file if requested.

config/routes.rb

@@ -1,4 +1,7 @@
 Rails.application.routes.draw do
+  # Liveness only: 200 when Rails boots successfully, 500 otherwise.
+  get "up" => "rails/health#show", as: :rails_health_check
+
   # This is a blank app! Pick your first screen, build out the RCAV, and go from there. E.g.:
   # get("/your_first_screen", { :controller => "pages", :action => "first" })
 end

render.yaml

@@ -5,6 +5,7 @@ services:
     plan: free # make sure to set this to free or you'll get billed $$$
     region: ohio # set this to the SAME region as your database, near your users (Supabase "East US (Ohio)" = ohio) to avoid slow cross-region queries
     dockerfilePath: ./Dockerfile
+    healthCheckPath: /up
     envVars: # this section sets some ENV variables needed by Render for deployment
       - key: SECRET_KEY_BASE
         generateValue: true
@@ -15,8 +16,6 @@ services:
         value: "0" # Puma single mode (no forked workers); greater value causes OOM on 512 MB free tier
       - key: RAILS_MAX_THREADS
         value: "3" # Cap threads to reduce memory
-      - key: MALLOC_ARENA_MAX
-        value: "2" # Reduce memory fragmentation
       - key: SOLID_QUEUE_IN_PUMA
         value: "true" # Run background jobs in same process
       - key: BUNDLE_WITHOUT

spec/jobs/application_job_spec.rb

@@ -0,0 +1,7 @@
+require "rails_helper"
+
+RSpec.describe ApplicationJob do
+  it "defers enqueues until the surrounding transaction commits" do
+    expect(described_class.enqueue_after_transaction_commit).to be(true)
+  end
+end

spec/requests/health_spec.rb

@@ -0,0 +1,9 @@
+require "rails_helper"
+
+RSpec.describe "Health check", type: :request do
+  it "reports that Rails booted" do
+    get "/up"
+
+    expect(response).to have_http_status(:ok)
+  end
+end